Computer displays generally update the image on the display sixty times in one second, i.e., with an update rate of 60 Hertz (Hz). Several computer displays allow this rate to be set within a range of possible rates, such as 48 Hz, 50 Hz, 59.94 Hz, 72 Hz and so on.
When video is played back on a computer, a sequence of images, called frames, is displayed on the computer display at a desired playback rate or frame rate. Video typically has frame rates of 24 Hz, 25 Hz, 29.97 Hz, and others. Video can be from movies, animation, games and the like
For playback of movies, the computer display is preferably set at a refresh rate that is an integer multiple of the frame rate of the video being played back. Otherwise, frames are repeated non-uniformly so as to produce an average frame rate matching the refresh rate of the display. For example, when playing video with a frame rate of 24 Hz on a display with a refresh rate of 60 Hz, some frames are repeated three times, and other frames are repeated only two times, resulting in a frame rate of 60 Hz. The non-uniform repetition of frames is visible and undesirable. Also, a display with a higher refresh rate consumes more power.
Video games have a similar problem. Video games align rendering with when frames can be displayed on the screen to prevent tearing and stuttering artifacts. Because of this alignment, if a game is only able to render at a speed that is less than the refresh rate, then a renderer for the game can be implemented in several ways. In some implementations, stuttering and tearing artifacts are allowed to occur. Another alternative is to render at a non-integer multiple of the frame rate and match frames to the nearest monitor frame. In other implementations, rendering can be throttled to the next factor of the refresh rate. For example, if rendering can only occur at 55 frames per second and the refresh rate is 60 frames per second, then the game renders at 30 frames per second. This pattern continues: if rendering can only occur at less than 30 frames per second, then rendering is performed at 20 frames per second. If the game can render at 55 frames per second, then by changing the refresh rate to 55 Hz from 60 Hz, the game can be displayed at 55 frames per second instead of 30 frames per second, resulting in a more pleasing visual experience.